Militarily, pull a fast one for Trump? (8)
I believe the answer is:
Here is my best explanation:
'trump?' is the definition.
('outflank' can be a synonym of 'trump')
'militarily pull a fast one' is the subsidiary indication.
I cannot quite see how this works, but
'a' could be 'an' and 'an' is present in the answer.
This may be the basis of clue (or it may be nonsense).
'for' is the link.
(Other definitions for outflank that I've seen before include "Get the better of, especially by surprise action", "Move round (enemy's) side", "Move around (an enemy's forces)", "defeat" and "Pass around the side of".)